Symmetry of LaAlO3 nanocrystals as a function of crystallite size

Properties of LaAlO3 nanocrystallites obtained by the precipitation method, doped with praseodymium and chromium ions were examined by spectroscopic means. Raman spectroscopy, high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and electronic spectroscopy proved that symmetry of LaAlO3 crystallites depends on their size. At room temperature the smallest obtained crystals (average size ∼5 nm) have cubic symmetry, while the largest ones (average size over 110 nm) exhibit rhombohedral symmetry. Possible explanations for this phenomenon are discussed.

Graphical AbstractThe 77 K emission spectra of LaAlO3:Pr3+ nanocrystallites codoped with Cr3+ as a function of the annealing temperature. Intensities were normalized to the maximum of the 3P0→3H4 transition. The R line at 13633 cm−1 vanish with decreasing the nanocrystals size and is absent for the smallest ones.Figure optionsDownload full-size imageDownload as PowerPoint slide